Spark plug



Nov. 8,1960 A. c. HASTINYGSHJR-V 2,959,703

SPARK'PLUG Filed Feb. 20. 1958 Invent Per: 56

Agent ARTHUR C. HAST/ JR of modification for use in'other plugs.

SPARK PLUG Arthur C. Hastings, Jr., Islington, Ontario, Canada Filed Feb. 20, 1958, Ser. No. 716,481

6 Claims. 01. 313-145 This invention relates to an improved spark plug for internal combustion engines with particular reference to improvements in the mounting of the centre electrode thereof; the present application being an improvement of my co-pending application Serial Number 545,489 now matured to United States Patent Number 2,833,950.

The centre electrode of a spark plug consists, basically and essentially, of an elongated wire conductor threaded through a somewhat shorter insulating sleeve of ceramic or vitreous material. Although tests and experience tend to show that the employment of a thin-walled sleeve in such electrode is conducive to better engine performance, prior mountings of the said centre electrode in the spark plug dictated the use of thick and massive sleeves with corresponding reductions in the efficiency of said prior plugs.

It is therefore a general object of the invention to provide a spark plug which is capable of improved performance in use.

Another object of the invention is to provide improvementsin the mounting of said centre electrode permitting the use of a thin-walled sleeve insulator therein.

A still further object of the invention is to provide a spark plug which is simple and economical to make and eflicient and durable in use and one which will have wider applicability permitting the expedient use of one type of plug in a wide variety of engines.

It is also an object of the invention to provide a present spark plug with terminal facilities enabling and contributing to the herein visualized simplicity of spark plug manufacture; said terminal being, however, also capable The foregoing and other more or less broad objects of the invention which will duly appear are generally achieved by providing a spark plug comprising a tubular metal housing adapted for installation in an internal combustion engine and having an upper cup and a lower chamber with an open mouth; a ground electrode carried by said housing adjacent said chamber mouth; a tubular shell of insulating material forming an extension of said cup; an elongated centre electrode within and in co-axial relation to said housing and with one of its ends in spark gap relation to said ground electrode; a terminal at the other end of said centre electrode, and insulating means within the cup and shell investing said centre electrode, integrally bonding it to the shell and the cup and maintaining it in the aforesaid co-axial and spark gap relation within said housing; said insulating means having been composed of a substance initially capable of being molded within said housing and shell and formed into a solid possessed of the requisite mechanical, thermal, electrical and bonding properties; all as will appear from the hereinafter following description of the elements, parts, methods and principles constituting the invention, a preferred embodiment whereof is herein described and illustrated in the annexed drawing wherein like reference States PatentO 2. devices refer to like parts of the various views and wherein:

Fig. 1 is a vertical elevation of a present spark plug with certain parts broken away to expose details of the interior structure thereof,

Fig. 2 is a somewhat reduced view of a modified terminal device for the spark plug of Fig. 1,

Figs. 3 and 4 are sectional views showing two successive steps in the method of manufacturing the present spark plug, and

Figs. 5 and 6 are cross-sectional views of the present spark plug respectively along lines VV and VIVI in Fig. l.

The pre-fabricated parts which are assembled to form the spark plug of Figure 1 consist essentially of the following three, namely; the centre electrode E; the tubular housing H; and the shell to be described.

Said centre electrode E, in turn, comprises an elongated wire conductor 10 whose lower or critical portion, at least, is passed through and enclosed by a somewhat shorter insulating sleeve 11; said wire 10 having a pointed terminal 12 at its top and an enlarged tip 13 at its bottom end which is one abutment for'the bottom of the sleeve 11. As seen, in Fig. 1, the upper part of the wire 10 projects through the top of the sleeve 11 and is spread at its point of emergence to provide a top abutment 14 for the sleeve 11.

Said housing H'is an open-ended metal tube having an integral interior partition 20 with a central passageway 21 through which the lower portion of the slightly undersize central electrode E extends into an open-mouthed lower chamber 23 constituted by a skirt 23 depending from the partition 20 which also provides a plane but preferably domed ceiling for the said lower chamber 23; said skirt 23 being exteriorly screw-threaded to adapt the said housing H for installation in an engine.

The walls of said housing H also rise above the partition 20 to form a shallow cup 25 adapted to accommodate the base 26 of a molded tubular shell 26 of insulating material whose cross-sectional span is progressively reduced in steps but whose walls are of substantially uniform thickness from the base to the top thereof; a thinned rim 27 of said housing walls extending above the shell base 26 being adapted to be upset to clamp and contain said base 26' against the partition 20.

' The assembly of the foregoing parts is preferably effected in the following manner, that is to say, the centre electrode E is placed in the slightly oversize passageway 21 with its bottom tip 13 resting on a spacer 30 clipped onto the ground electrode 31 carried by housing H which co-operates with said tip 13 to form a spark gap at the mouth of the lower chamber 23; the thickness of the material forming the spacer 30 corresponding to the dimensions of the spark gap.

When. the centre electrode E is in place, a dam 32 is formed on the partition 20 about the sleeve 11 which extends therethrough into cup 25; a similar dam 32 being formed around the emerging wire 10 at the top of sleeve 11. Following these precautions, a measured quantity of liquid plastic 33' (to be described) is poured into the cup 25 after which the shell 26 is positioned as in Fig. 1 with V the terminal 12 of wire 10 protruding therefrom.

suitably upsetting the thinned rim 27 of the housing H in the manner noted.

The foregoing assembly is then heat-cured to solidify the plastic liquid 33 into a solid core 33 hermetically bonded to the wire 10, sleeve 11, shell 26 and housing H.

Plastics adapted to be converted by heat from a liquid to a solid having the mechanical, thermal and bonding properties of the present core 33 may be selected from the group known as silicone plastics sold, for example, under the trademark Silastic whose characteristics are variable according to the proportions of the hardener and/or filler incorporated therein by the maker thereof.

Another substance marketed under the brand Epoxy has also proven acceptable for the purpose herein visualized as have some compounds of nylon.

At any rate, the composition of the plastic substance utilized is such as to render it co-efficient of thermal expansion approximately equal to that of the shell 26 so that the respective expansion and/ or shrinkage thereof will be more or less equalized. In addition, the component substance of the core 33 should be capable of bonding with the metal of housing H to form a hermetic seal therewith and must be slightly elastic to compensate for any difier ences obtaining therebetween in their relative rates of expansion and shrinkage; all of which properties may be embodied and found in any of the aforenoted materials.

While dealing with the problem of thermal expansion and contraction it is deemed opportune to note that the wire is slightly undersize for the bore of sleeve 11 so that it will not burst said sleeve 11 upon expansion.

It will now be noted that the spark plug construction herein set forth obviates all need for any unyielding mechanical grip on the sleeve 11 such as was characteristic of the prior art. The cross-sectional dimensions of said sleeve 11 are therefore herein influenced only by electrical and not by mechanical considerations. Thus if glass or porcelain is the component substance thereof its walls may be substantially thinner than they customarily were in the prior art; this being productive of other benefits such as, namely, increased resistance to thermal shock and also a reduced obstruction of the lower chamber 23 which permits greater air circulation therein with it attendant cooling of the centre electrode E which, in turn, prevents overheating thereof and, consequently, pre-ignition.

It is the view of some authorities that the optimum performance of a spark plug in an engine is dependent upon the maintenance of its centre electrode temperature within a certain more or less critical range. Thus, a temperature in excess of this range is believed to be conducive to preignition or premature explosion with an attendant loss of etliciency. Conversely, if the said temperature is not reached, a condition akin of reduced carbon combustion is thought to follow and to be conducive to fouling.

Bearing in mind that a massive insulator takes longer to heat and/or cool, it will be understood that a spark plug having a centre electrode equipped with such insulator will find difiiculty both in attaining and in maintaining the required temperature.

Thus, in an idling or a cold engine, a massive insulator in the explosion chamber of the plug will prolong the conditions which are conducive to fouling and, in a hot engine, will be difiicult to cool below the pre-ignition point.

Despite that the present core 33 forms a mass around the upper part of the centre electrode B, it does not senously offset the advantages accuring from the use of a thin-walled sleeve in the lower chamber 23 inasmuch as the temperature characteristics affecting the operation of a spark plug are those of the lower portion of the centre electrode E in what might be called the combustion or explosion chamber of the plug.

At all events, the partition also serves as a heat barrier; capturing the heat of the centre electrode E in passageway 21 and conducting it to the exterior, for which reason the said partition 20 may be thickened as shown in the drawing.

Reverting now to the spark plug terminal 12 of Fig. 1, it will be seen to comprise a sharpened point on the top of the wire 10 which projects from the reduced top of the shell 26.

Being sharpened and pointed said terminal 12 of Fig. 1 is adapted to transfix an ignition Wire 35 entering and crossing flexible hood 36 which is dimensioned and otherwise adapted to cap the shell 26.

Alternately, a more conventional type of terminal 12 of Fig. 2, being a hollow device, may be partially inserted into shell 26 through its top opening to electrically engage the wire 10 which may be shortened for the purpose; the liquid 33 poured into cup 25 being sufficient, when displaced, to reach and solidify around said terminal 12 within the cavity of shell 26.

At all events, it will be noted that the present terminal in either of the forms herein given is maintained in a more or less rigid state by the core 33, thus eliminating the need for screw-threading, nuts and so forth which were characteristic of the prior art; said terminal being peculiarly adaptable for use with the present mounting.

Since certain changes may be made in the spark plug structure herein visualized without departing from the scope of the invention, it is intended that all matter contained in the foregoing description shall be taken as illustrative rather than as a limitation of the inventive ideas herein expressed.

What I claim as my invention is:

1. A spark plug comprising a tubular metal housing adapted for installation in an internal combustion engine and having an upper cup and a lower chamber with an open mouth; a partition with a central communicating passageway separating said cup and said chamber; a ground electrode carried by said housing adjacent said chamber mouth; a tubular shell of insulating material forming an extension of said cup; an elongated centre electrode slightly smaller than said passageway extending therethrough within and in co-axial relation to said housing and with one of its ends in spark gap relation to said ground electrode, a terminal at the other end of said centre electrode, and insulating means within the cup and shell investing said centre electrode integrally bonding it to the said shell, cup and partition and maintaining it in the aforesaid co-axial and spark gap relation within said housing, said insulating means being composed of a substance initially capable of being molded within said housing and shell and formed into a solid possessed of the requisite mechanical, thermal, electrical and bonding properties.

2. The device set forth in claim 1 wherein said centre electrode comprises a conductor wire and a thin-walled insulating sleeve therefor enclosing and insulating said wire for at least that part of its length within said passageway and said lower chamber.

3. The device set forth in claim 1 wherein said shell has an internal capacity less than that of said cup.

4. The device set forth in claim 1 wherein said centre electrode comprises a conductor wire and a thin-walled insulating sleeve therefor, loosely enclosing and insulating said wire for at least that part of its length within said passageway and said lower chamber.

5. A spark plug comprising a tubular metal housing adapted for installation in an internal combustion engine and having an upper cup and a lower chamber with an open mouth; a ground electrode carried by said housing adjacent said chamber mouth; a tubular shell of insulating material forming an extension of said cup; an elongated relatively slender centre electrode within and in co-axial relation to said housing and with one of its ends in spark gap relation to said ground electrode, said centre electrode including a conductor and a thin-walled insulator sleeve therefor; a terminal at the other end of said centre electrode, and insulating means within the cup and shell investing said centre electrode, integrally bonding it to the shell and the cup and maintaining it in the aforesaid coaxial and spark gap relation within said housing; said insulating means being composed of a substance initially capable of being molded within said housing and shell and formed into a solid possessed of the requisite mechanical, thermal, electrical and bonding properties.

6. A spark plug comprising a tubular metal housing adapted for installation in an internal combustion engine and having an upper cup and a lower chamber with an open mouth; a partition with a central communicating passageway separating said cup and chamber; a ground electrode carried by said housing adjacent said chamber mouth; an elongated centre electrode slightly smaller than said passageway extending therethrough within and in co-axial relation to said housing and with one of its ends in spark gap relation to said ground electrode, said centre electrode including 'a conductor wire and an insulator sleeve therefor enclosing said wire for at least that part of its length within said passageway and lower chamber; a terminal at the other end of said centre electrode, and insulating means within and extending exteriorly of said cup investing said centre electrode, integrally bonding it to the said cup and partition and maintaining it in the aforesaid co-axial and spark gap relation Within said housing; said insulating means being composed of a substance initiall-y capable of being molded within said housing and formed into a solid possessed of the requisite mechanical, thermal, electrical and bonding properties.

References Cited in the file of this patent UNITED STATES PATENTS 916,313 Herrington Mar. 23, 1909 918,726 Bartl Apr. 20, 1909 1,192,602 Bond July 25, 1916 1,962,968 Nowosielski June 12, 1934 1,977,938 Excoflier Aug. 20, 1934 2,069,951 Hastings Feb. 9, 1937 2,309,236 Burrell et al. Jan. 26, 1943 2,311,647 Doran Feb. 23, 1943 2,351,543 Race June 13, 1944 2,356,053 Hastings et al Aug. 15, 1944 2,453,048 Tognola et a1. Nov. 2, 1948 2,633,116 Ingram Mar. 31, 1953 2,833,950 Hastings May 6, 1958 

